Kinetics for the association of inner histones and 140 base pair (bp) DNA in 0.6 M NaCl have been determined. An initial fast reaction leads to folding of 75% of the DNA; the remaining folds over a several hour period with exponential kinetics, independent of concentration. Mechanisms have been examined, and one, involving transfer of an octamer of histones from core particle to naked DNA, judged to be most consistent with the experimental data. Similar studies of histone-DNA association have been performed with trypsin-treated histones. Although they lack the basic amino-terminal region, these histone can fold DNA into a compact structure. Extensions of previous studies have substantiated the role of an H3 plus H4 tetramer in providing the nucleus for folding DNA into a core particle-like structure. The accessabilities of the inner histones to chemical modification by a nonspecific chemical probe have been determined at different salt concentration. The state of association of histones in 2 M NaCl has been studied by several physical methods; results suggest a tetramer-octamer equilibrium. The octamer portion of these histones apparently exists in a different structure from the octamer present in the core particle, since the crosslinked solution octamer does not refold DNA efficiently.